Tính a) (2x-y+2)^2 b)(xy/2-x/3).(xy/2+x/3) ko lm tắt nha

a) $(2x-y+2)^2$

$=(2x-y+2).(2x-y+2)$

$=[(2x-y+2).2x]-[(2x-y+2).y]+[(2x-y+2).2]$

$=[4x^2-2xy+4x]-[2xy-y^2+2y]+[4x-2y+4]$

$=4x^2-2xy+4x-2xy+y^2-2y+4x-2y+4$

$=4x^2+y^2+(-2xy-2xy)+(4x+4x)+(-2y-2y)+4$

$=4x^2+y^2-4xy+8x-4y+4$

b) $(\dfrac{xy}{2}-\dfrac{x}{3})(\dfrac{xy}{2}+\dfrac{x}{3})$

$=[(\dfrac{xy}{2}-\dfrac{x}{3}).\dfrac{xy}{2}]+[(\dfrac{xy}{2}-\dfrac{x}{3}).\dfrac{x}{3}]$

$=[\dfrac{x^2y^2}{4}-\dfrac{x^2y}{6}]+[\dfrac{x^2y}{6}-\dfrac{x^2}{9}]$

$=\dfrac{x^2y^2}{4}-\dfrac{x^2y}{6}+\dfrac{x^2y}{6}-\dfrac{x^2}{9}$

$=\dfrac{x^2y^2}{4}+(-\dfrac{x^2}{y}+\dfrac{x^2y}{6})-\dfrac{x^2}{9}$

$=\dfrac{x^2y^2}{4}-\dfrac{x^2}{9}$